URBANA, ILLINOIS
Maize Genetics Cooperation Stock Center

Mutable r1 haplotype-specific aleurone color enhancers Fcu and arv-m594 map to the same location.

—Stinard, PS

In last year’s MNL (MNL 78:63–64), we reported that the mutable r1 haplotype-specific enhancers of aleurone color Fcu and arv-m594 both map to the long arm of chromosome 2. In order to help determine whether these two factors might be identical, we undertook a linkage test to determine whether they map to the same chromosomal location. To perform this test, we crossed a homozygous r1-g Fcu line (provided by Peter Peterson of Iowa State University) by a homozygous r1-g arv-m594 line (provided by Jerry Kermicle of the University of Wisconsin), and crossed the F1 as males onto the reporter haplotype R1-r(Venezuela559-PI302355). Both parental classes and the Fcu arv-m594 recombinant class would be expected to produce sectored kernels. The recombinant class lacking both factors would be expected to be stable (non-sectored). The kernels on the backcross ears were scored for presence or absence of aleurone color sectoring. The results are presented in Table 1.

Seven stable putative crossover kernels were recovered and planted the following season, and the resulting plants selfed and outcrossed to R1-r(Venezuela559-PI302355) testers. All outcrosses segregated for sectored kernels, indicating that the stable kernel phenotypes were not due to recombination between Fcu and arv-m594. Four of the selfed ears produced only colorless kernels, indicating that the reason for their stability was a mutation from R1-r(Venezuela559-PI302355) to r1 in the tester parent. The remaining three segregated for sectored kernels in the self, indicating that they carried all factors needed for sectoring, but did not produce any sectors in the limited aleurone area of those particular exceptional kernels.

The one full colored putative revertant kernel recovered from these tests proved not to be a true germinal revertant, and produced sectored kernels in both self and outcross.

Thus, there were no crossovers in a population of 2,233 kernels, indicating a separation of less than 0.09 centiMorgans between Fcu and arv-m594.

A third independently isolated mutable r1 haplotype-specific enhancer of aleurone color, arv-m694 (isolated from Kermicle’s R1-r(Venezuela694#16037) stock), is also known. Linkage tests between Fcu and arv-m694, and between arv-m594 and arv-m694, were performed in a manner analogous to that described above for Fcu and arv-m594. From the Fcu/arv-m694 tests, we obtained 8 stable kernels and 1 full colored kernel out of a population of 2,372 kernels (separation of 0.7 centiMorgans). From the arv-m594/arv-m694 tests, we obtained 4 stable kernels and 2 full colored kernels out of a population of 1,620 kernels (separation of 0.5 centiMorgans). Putative crossovers and revertants will be planted next summer and testcrossed to determine their genotypes.

Finally, a revertant of Fcu to a stable enhancer, Fcu-R2003-2653-6 (Stinard, MNL 78:64–65) was tested for linkage with a stable enhancer from the arv-m system, Arv-V628 (isolated from Kermicle’s R1-g(Venezuela628#16038) stock). We obtained 6 pale stable putative crossovers from a population of 1,887 kernels (separation of 0.6 centiMorgans). The exceptions will also be tested next summer.

The linkage tests described in this report indicate that the three mutable enhancers and the two stable enhancers of aleurone color are separated by less than one centiMorgan, and most likely map to the same location on 2L. Fcu was isolated from Cuna tribal maize collected in Unguia, Colombia (Gonella, JA and Peterson, PA. 1977. Genetics 85:629–645). The exact origin of arv-m694 is unknown, although it is from a Venezuelan accession. All three lines came to the United States through the Tulio Ospina Research Station, Instituto Colombiano Agropecuario, in Medellin, Colombia (Gonella and Peterson, 1977; Kermicle, personal communication). Whether the mutable enhancers are independent alleles, or whether they represent the isolation of the same allele from different sources, remains to be determined.

Table 1. Counts of sectored and stable kernels from the cross R1-r(Venezuela559-PI302355) × [r1-g Fcu × r1-g arv-m594].

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